Electric-circuit protective device



July 8, 1924.

D. K. LIPPINCOTT ELECTRIC CIRCUIT PROTECTIVE DEVICE- INVENTOR yam/01.0L/PP/A/'dft' Filed Dec. 9, 1919 as my 3,1924. p p

U N i Y 'S'T BATE-NT. OFFICE,

' x; jmrrmco rnor SAN rmcrscogcamronnm, assrcmon, BY mrnsm: 48-, Isrcmmn'rs, T GENERAL ELECTBIG comramr, A coarom'rron or NEW oax.

v To-dll whom it mag concern;

Be it known: that'I, DONALD K. LrPrIN com, a citizen of the UnitedStates, and a ELECTRIC-CIRCUIT PROTECTIVE DEVICE.

"Application filed December 9, 1919. Serial No. 343,483

resident of the city and county of San Fran 'cisco State of California,have invented certain new and useful Electric-Circuit ProtectiveDevices, of which the following is a specification. r f A The inventionrelates to devices for interrupting an electrical circuit containingelectrical apparatus when the temperature of the apparatus approaches adangerous value and particularlyto relayswhich are oper-' ated .toactuate tripping devices for openture is approached.

.The devices of my invention are operated by an increase in temperatureto or above a predetermined temperature, to actuate tripping devices,eithermechanically or electr1cally, to open an electric circuit.

fully reproduced, so that any condition or An object of the invention,is to provide a device in .which the temperature of the electricalapparatus, whether it be a motor, a. transformer or other apparatus, isfaithseries. of conditions of current flow which will produce adangerous temperature in the apparatus, will in the same time, producein the device a temperature which-will cause it to operate tointerruptthe circuit.

Anotherobject of the invention is to provide a device the heating curveof. which follows the heating curve of the apparatus being protected andwhich can be constructed to follow the mean heating curve or the hotspot heating curve ofthe ap paratus.

A further object of the invention isto provide a device which willoperate under shortcircuit conditions to immediately in- A furtherobject of the invention is to provide a device which provides protecetion against short circuiting conditions in the apparatus and at .thesame time provides the thermal protection and which followsthe heatcurve of-the hot spot of the ap aratus.

e invention possesses other advantageous features, some of which withthe foreoing, will beset forth at length in the folowing description,where I shall outline in full, that. form of the invention which I haveselected for illustration in the drawpairs.

I have found that three factors enter into ings accompanying and formingpart of in the claims,'may be embodied a plurality offorms. v p

The protective device of my invention,

when operating, that is, when current is flowing in the circuit, ispreferably substan apparatus being protected. Since the device tiallyso, a dangerous temperature in the apparatus will be accompanied by acorre-' sponding temperature in the device, and this temperature willcause the device to be actuated to open thev circuit, thereby precludingany further current flow. Bya dangerous temperature, I do not mean adestructive temperature, but rather, any temperature beyond which thecontinued safe operation of the apparatus is not assured. By virtue ofthis synthermal. relationship which obtains at all times during theoperation of the apparatus, it is possible to operate the apparatusonoverloads of large. or small magnitude, with the assurance that theapparatus will carry. the overload for the maximum possible period andthat the circuitwill be interrupted in advance of the production of adangerous temperature in the-apparatus- This permits the operator tooperate his apparatus at its maximum capacity, without fear of burnoutsand the consequent cost of idle equipment and re-' the equationwhichkdetermines thetemperature produced inelectrical apparatus,'these(factors being, heat generation, heat storage and heat emission, andthese three factors 1 must be of the same relative magnitude produce the'synthermal relation. Heat is the-temperature of a particular spot inthe apparatus being protected is considered, in

contradistinction to the mean temperature,

tially synthermal with the hot spot in the i and'apparatus aresynthermal' or substan ing the circuit when the dangeroustemperagenerated-by the flow ofcurrent through 4 :a resistance, heat isstored in any material or other apparatus, contains material whichpossesses heat storage capacity and to produce a synthermal orsubstantially synthermal protective device, provision must be made inthe device for heat storage.

The temperature of a body heated uniformly throughout its mass at auniform rate may be expressed quite accuratelyby the expression g r@.=r1-awhere Te is the temperature at any instant;

T the temperature of equilibrium, reached theoretically only afterinfinite time, but approached closely in a comparatively short period; tis the time during which heating has been taking place; 6 is the base ofthe 1 natural logarithms and 7c is a constant, based upon the ratio ofthe heat capacity of the body in question to its heat emission and deending numerically upon the units involved in the expression. If theheat is developed in a certain limited portion of the body and iscarried to the remainder of the mass by conduction, the expression forthe temperatureof the hot spot becomes a very complex expression, theexact mathematical treatment of which is very dificult. Under thiscondition'k is no-longera constant, but varies with the time, i. e. asthe heat is carried' throughout the mass, the proportion of heat storedto heat emitted is increased. If it be assumed that this increase isproportional to some power of the time 1 obtain the equation being about0.7. It is the magnitude of this- ,exponent nwhich determines the shapeof the heating curve as distinguished from its magnitude. In the deviceof my invention, 1t is possible, by proper proportioning and selectionof materials to vary n within wide limits thereby permitting constructedto be responsive to the tempera= 'ture of the apparatus as a whole; tothe temperature of the windings or to the temperature of some selectedportion of the windings, whichever'ma be' most suitable to the servicefor which the device is designed.

The device of my invention, which I have neonoie In this equation 12. isa fraction the device to \be termed a thermal relay, comprises a heatingelement, a heat storage element or heat ballast, a thermal responsiveelement, which in the present instance also serves as the heat storageelement and means responsive to the thermal responsive element whichfunctions to cause interruption of the electric circuit. The ballastreceives its heat preferably by conduction, from the heating. element,and I have so arranged the ballast with relation to the heating element,that the mean temperature integrated longitudinally to which theballast, (in this instance also the thermal responsive element) issubjected corresponds directly with or is the same as the temperaturewhich is produced in the hottest part of the destructible Figure 3 is avertical section through the relay showing a preferred form ofconstruction.

Figure 4 is "a diagrammatic representaticn of a three phase electriccircuit equipped with the relays of my invention and showmg.

one form of switch tripping circuit. It is not essential that the relaysbe connected through the specific tripping circuit shown, since anyother or known form of tripping circuit may be employed. i i

As I have stated before, the deviceflof my v invention not only operatesto interrupt the circuit when a dangerous temperature heavy overloads orlong continued small overloads or combinations thereof, but acts toimmediately open the circuit upon the presence of an abnormal excess ofcurrent in the circuit, such as may be produced by short circuitconditionsin the apparatus, improper connections or other causes.

The relay shown in the drawings comprises a body or mass 2 of heatstorage material having a fairly" hi h thermal conductivity and a largec6e cient of expansion, such as lead or zinc. It is of advantage to makethis body 2 either of pure metal or of an alloy which solidifies in theform of a solid solution. Inthose alloys in which the materialscrystallize out separately, the coefiicient of expansion a pears tochange with repeated heating an cooling, and altho this can be partlyover- 110 is approached in the apparatus due to short position byengage-ment of the cap with av suitable support, but may be supportedfrom the lower end when esired. ecured to the lower end of the body is acap 5,

which may be provided with an external thread adapted to be secured intoa supporting socket.

he body 2 is provided with a transverseslot or opening 6 at.its upperportion and below the slot is formed with a cylindrical bore, so thatthe lower or main portion of the body is annular in shape. Disposedwithin the annular portion of the body is a heating coil 7, which ispreferably coaxial with the body and disposed at approximately theradial center of mass of the heat stortge element. The heating coil orheating element is preferably formed of copper wire covered withsuitable insulation which ordinarily may be ordinary cotton insulationalthough other forms of insulation, such as enamel may be employed whenhigh tem eratures are to be encountered. The coil 1s formed and the body'2 is cast around the coil, so that the body makes a tight and veryclose thermal contact with-the coil, so that heat conduction between thetwo elements is raised to its possible maximum.

In practice I prefer to wind the heating coil on a threaded spacing core10 which is then spaced in a mold and the body 2 cast around it. Thecore 10 produces the proper spacing of the turns of the coil and insuresthe proper positioning of the 'coilin the body. The core is of the samematerial as the body and when the molten metal is poured into the mold,unites with the poured metal, forming a functionally integral body. Thebody is cast in chillsso that the heat of the metal is rapidly conductedtherefrom and under these circumstances I have found that plain cottoninsulation onthe wire of the heating coil was not charred or in anymanner altered. The ends of the heating coil are brought out through thecap 3 and are provided with suitable terminals- 8 for connection in theelectric circuit. The metal of the body has a large coefiicient ofexpansion so that variations in temperature of the body producevariations in the len h thereof, i. e., variations in the distanceetween the caps 3 and 5.

Disposed in the bore formed within the annular body and preferablyfreely movable with respect to the body, is a bar or rod 9, of materialhaving a low eoefiicient of expension, such as nickel steel. For reasonspansion is low in comparision with the 00- I efiicient of expansion ofthe metal of the body 2, the variation in length of the body due'totemperature changes is manifested between the cap "3 and the upper endof the rod 9 that is, the upper end of the rod 9 moves substantiallycoincidently and equally with the lower end of the body. The rod 9 isfreefrom the body 2, but is in close thermal contact therewith, so thatthe rod also acts as a heat storage element. The heat storage element istherefore a composite structure consisting of the body 2 and the rod 9.v

. Secured to the cap 3 and lying within the slot 6 in: the body 2 is acontact head 12, formed integral with the binding post 13.

The head '12 forms an upper spring seat..

Secured to and insulated from the upper end of the rod 9 is a lowerspring seat 14.

Arranged between and engaging the two spring seats is a thin metallicflat spring 15 to which is secured a contact 16. In the constructionillustrated, the spring is normally bowed and is straightened out by anincrease in temperature of the body. Extending transversely through thebody 2 and into the slot 6, is a contact screw 17, carrying a contact 18which is engaged by the contact 16 when the temperatureof the bodyreaches a predetermined value. The screw 17 is adjustable in the planeof movement of the spring, but ordinarily it is set and fixed when thedevice is rated. In this construction the contacts are normally out ofengagement and are brought into contact by a rise in temperature to apredeterminal value, but the screw may be arranged on the other side ofthe spring so that the contacts are normally inengagement and areseparated by the rise in temperature.

The device, as thus far described, is a thermal relay and when shortcircuiting protection is not desired, it may be built as heretoforedescribed. The device as shown in the drawings however also offers shortcircuiting protection. Arranged within the cap 5 and bearing against theadjusting screw 21 is a spring 22, which bears at its upper end againstthe spring plate 23, which is held against further vertical movement bythe internal annular shoulder 24 on the cap 5. The rod 9, which I havestated is formed of magnetic material, is provided on its lower end witha ntek 25 which extends through the aperture in the shoulder 24 andrests against the plate 23. The rod 9 is therefore. held in raisedposition by the spring 22 and may be depressed a limited distance,the'distance' 'being limited by the lower end of the rod. The heatingcoil 7 is so disposed with relation to the rod 9, that the flux producedby the flow of current through the heating coil exerts a downward pullon the rod 9. The spring 22 0pposes this pull and is so adjusted, thatthe rod is pulled down a ainst the action of.

the spring, when a ,pre etermined abnormalcurrent flows through theheating coil. Consequently an abnormal current, such as is produced byshort circuit conditions in the apparatus, will immediately cause therod to be depressed, bringing the contacts 16 is and 18 into engagement.The device of my invention may be employed with any suitable formoftripping' circuit, so that the engagement of the contacts operates tothrow the tripping device into operation. In the present instance I haveshown the devices of my invention installed in a three phase three wirecircuit connected to the motor 26, which is the' apparatus to beprotected. The circuitis provided with a three blade switch 27v which isheld in the closed position by a latch 28. The-switch is provided with asuitable opening spring (not shown) for opening the switch when thelatch is released. Two devices A and B of my inveiition are arranged in.the two outer le s 31-32 of the cir uit,

withthe heating 001 s 7 in series in the egs, so that the current in thecircuit 1 flows through the heatingcoils, and these devices arepreferabl placed on the motor side of the switch. onnected across thelegs 31-32 of the circuit between themotor' and the switch is a circuit33, containin a solenoid 34 which in this instance is a' ow voltagecoil. The'plunger 35 in the solenoid is-.arran ed in operative positionwith respect to the latch 28, so thatupon a reduction of line voltage toa predetermined value,'.the solenoid drops, opens the latch and releasesthe switch. In this arrangement, the devices are arranged, so thatengagement of the contacts 16 an 18, short circuits the low voltage coil34, releasing the plun er and permitting the switch to open. The indingpost 13' of the .device A is connected to the circuit 33 on, the

. opposite side of the coil34 from the leg 31 and the binding post 13 ofthe device B is connected to the circuit 33 on the opposite side of thecoil 34 from the leg 32. The contact screw 17 is embedded in andconsequently electrically connected to the body 2 and the screw 17 ofthe device A is connected directly or mediately through the body withthe adjacent leg of the circuit 33 and the screw 17 of the device B isconnected to the adjacent leg of the circuit'33, The contacts 16 and 18in each device aretherefore connected to the circuit 33 on oppositesides of .the solenoid 34, so that when the contacts of either devicemove into engagement with each other, the solenoid is short circuitedand the switch opened. The opening of the switch disconnects the motorand the devices from thesupply circuit, so that there is no current atthe contacts when they subsequentlyseparate, due tothecooling of the;body. A resistor 35 is arranged in the circuit 33 to limit the currentthrough the contacts of the device.

It is understood that. the devices of my .invention are not limited inuse to the tripping circuit shown, but may be employed in connectionwith any sutable circuit or device, for opening the electric circuit.'The present circuit incorporates the advantages of a low voltagerelease, which isdesirable, and for that reason I have shown suchcircuit. The devices may also be constructed, as set forth'hereinb'efore, to open or close a tripping circuit as a dangeroustemperature is approached. f

There are several methods of constructing the device so that it willfollow any desired form of hot spot curve or other desired curve orform, such as varying the construction of the device or relation of thearts so that a rounding the heating coil as shown in Figure 1 or bysurrounding the body with a tube 36 of some'material, the ratio of thespecific heat of which toits thermal conductivity differs from that ofthe body 2. Such tube may be composed of pressed fiber or paper.

Many methods, such as providing radiating fins for a portion of the bodyor surrounding'a portion of the body with heat insulating material, maybe employed to vary the value of am the above equation to any desiredextent or to follow equations of even more complex form. The rate ofheat generation, heat emission, conduction, spe-' cific heat and henceheat storage, are separately variable, so that any desired result maybeobtained.

I claim:

cuit containing electrical apparatus, com- -prising a metallic thermalresponsive device of large mass and a heating element adapted to beplaced in circuitwith the apparatus embedded in said mass.

2. A protective device for an electric circuit containing electricalapparatus, comprising a heat storage element formed in two parts havingdifferentcoeflicients of expan- 1. A protective device for an electriccirsion, means operative by anincrease in temperature of said elementtoa predetermined temperature, to perform a controllin function, and aheating element adapts to be placed in circuitwith the apparatusdisposed in thermal communication with said heat storage element.

trolling said circuit.

3. A protective device for an electric circuit containing electricalapparatus, comprising a heat storage element formed in two partshavingdiiferent coeflicients of expansion, means operative by anincreasein temperature of said element to a predetermined temperature,to perform a controlling function, and a heating element embedded insaid heat storage element adapted to be placed in circuit .with theapparatus.

4. A protective device for an electric circuit containing electricalapparatus, com-" prising a metallic heat storage element, a heating coilembedded in said element, a rod having a different coeflicient ofexpansion than said element arranged within said element and meansoperative by different variations in length of said element and rod dueto a rise in temperature, to a predetermined temperature, to perform acontrolling ction. p) 5. A protective device for an electric circuitcontaining electrical apparatus, comprising a heating coil adapted to beplaced in circuit with the apparatus, a metallic heat storage element.in which said .coil is embedded, and means operative by variation insize of said element due to an increase in temperature to a giventemperature, to control the circuit with which the device is associated6. A protective device for an electr' circuit containing electricalapparatus, comprising a heating coil adapted to be placed 1n circuitwith sald apparatus, a heat storage element in which said coil isembedded, means operative by variations in temperature of said heatstorage element for controlling the circuit with which the deviceisassociatedand means operative by the magnetic eiiectof current in thecoil for con- 7. A protective device for an electric circuit containingelectrical apparatus, comprising a heat storage element, a heating coiladapted to be placed in circuit with theapparatus and embedded in saidelement,

. means operative by variations in temperature of said heatstorageelement for controlling the circuit with which the device v isassociated, a movable body within said element subjected to the magneticfield of said coil, and means operative by the movement of the body withrespect to the element for controlling said circuit.

8. A protective device for an electric circuit containing electricalapparatus, comprising a cylindrical metallic body. closed at its lowerend, a heating EH11 embedded in said body, arod of less length than thebody dis osed within the body and resting a amst the lower end thereof,the coeflicient 0 expansion of the rod being other than that of thebody, so that variations in temperature of the body vary the distancebetween the upper end of the body and the upper end of the rod, andmeans actuated by such variation in distance adapted to control thecircuit.

9. A protective device for an electric circuit containing electricalapparatus, comprising a cylindrical metallic body closed at its lowerend, a heating coil embedded in said body, a rod of less length than thebody disposed within the body and resting against the lower end thereof,the coefficient of expansion of the rod being other than that of thebody, so that variations in temperature of the body vary the distancebetween the upper end of the body and the upper end 0 the rod, a flatsprin interposed between the upper end of the ody and the upper end ofthe rod, a contact carried by said spring, and a contact carried by saidbody normally out of contact with said first mentioned contact, saidcontact adapted to be closed-at a predetermined temperature.

10. A protective device for an electric cir cuit containing electricalapparatus, comprising a cylindrical metallic body closedat its lowerend, a heating coil embedded in said body, a rod of less lengththan thebody disposed within the body and resting against the lower end thereof,the coefiicient of expansion of the rod being other than that of thebody, so that variations in temperature of the body vary thedistancebetween the u per end of the body and the upper end 0? the rod,a spring interposed between the upper end of the body and the upper endof the rod, a contact on said spring, a fixed contact adapted to beengaged by said spring contact a'nd an electric control circuitconnected to said contacts. 11. A protective device for an electriccircuit containing electrical apparatus, comprising a cylindricalmetallic body closed at its lower end, a heating coil embedded in saidbody, a rod of less length than the body disposed within the bod andresting against the lower end thereo the coefiicient of expansion of therod being other than that of the body, so that variations in temperatureof the body vary the distance between 1 said -screw adapted to beengaged by said spring contact and an electric control c1rcuit connectedto said contacts.

12. A protective 'device'for an electric circuit containin electricalapparatus, comprisin a cy indrical metallic body closed at its lowerend, a heating coil embedded in said body, a rod of less length than thebody dis osed within the body and restin againstt e lower end thereof,the

coeflicient of expansion of the rod being 25 having, a differentcoeflicient of expansion other than that of the body, so that variationsin temperature of the body vary the distance between the upper end ofthe body and the upper end of the rod, a spring interposed'between theupper end of the body and the upper end of the rod and insulated fromsaid body and rod and means actuated by movement of the spring adaptedto open the electric circuit.

cured to the upper end of said body, a cap secured to the lower end ofsaid body, a rod of less length than said body disposed therein andsupported by the lower cap, said rod than the body, a bowed springinterposed between the upper cap and the upper end of the rod, a contactcarried by said spring, and a. cpntact carried by said body and adaptedto be engaged on movement of the spring by said first contact to performa controlling function with respect to the circuit;with which the deviceis associated.

' 15. A protective device for an electric circuit containing electricalapparatus, comprising a thermal responsive device consisting of twometallic elements having different coeflicients ,of' expansion, one ofsaid elements being of magnetic material, a heat ing coiladapted to beplaced in circuit with the apparatus embedded in one element andsurrounding the other element and so placed that the magnetic field ofthe coil exerts a pull. on said magnetic element, and means operative bya movement of the end of the magnetic element for performing acontrolling function with respect to the circuit with which the deviceis associated.

16. A protective device for an electric circuit containing electricalapparatus, comprising a ,thermal responsive device havin a large heatstorage capacity, a heating co' embedded in said thermal responsivedevice,

means operative by variations in temperature of said thermal responsivedevice for opening said circuit,-and means operative by the magneticeffect of the current in the coil performing a "controlling functionwith respect to the circuit with which the device is associated. l

17 A protective device for an electric circuit containing electricalapparatus, comprising a thermal responsive device havin a large heatstorage capacity, aheating coi embedded in said thermal responsivedevice,

and means operative by an increase in temperature of said device to apredetermined temperature to control the circuit with which the deviceis associated and by an increase in the magnetic flux of said coil to apredetermined value to control the circuit with which the device isassociated.-

18. A protective device for an electric circuit containing electricalapparatus, comprising an annular metallic mass, a heating coil adaptedto be placed in circuit with the apparatus embedded in said mass, amagnetizable plunger having a different coefllcient of expansion thansaid mass disposed within the chamber at the center of said annularmass, the magnetic center of said plunger being spaced longitudinallyfrom the magnetic center of said coil, a spring supporting said plungerand means operative by the movement of the upper end'of the plunger forcontrolling the circuit with which the device is-associated.

19. A protective device for an. electric circoil adapted to be placed incircuit with the apparatus embedded in said mass, a ma netizable plungerhaving a diiferent coe cient of expansion than said mass disposed withinthe chamber at the "center of said annular mass, the magnetic center ofsaid plunger being spaced longitudinally from the magnetic center ofsaid coil; a cap secured to the lower end of-said mass, a spring in saidcap on which) said plunger rests, means for limiting the movement of theplunger and means operated by the movement of the plunger forcontrolling the circuit withwhich the device is associated.

20. A protective device for an electric circuit containing electricalapparatus, composed within the chamber at the centerof said annularmass, the magnetic center of said plunger being spaced longitudinally.

from the magnetic center of. said coil, a cap secured to .the lower endof the mass, 8.

spring in said cap against which the plun- 'ger bears, means for varyingthe compression of said spring, and means operated b the movement of theplungerfor contro lin the-circuit with which the device is associated. py

21. A protective device for an electric circuit containing electricalapparatus, comprisin an annular metallic mass, a heating c011 adapted tobe placed in circuit with the apparatus embedded in said mass, amagnetizable plunger having a different 00- eflicient of expansion thansaid mass dischamber at the center of said annular mass, the magneticc'enter'of said plunger being spaced longitudinally from the magneticcenter of said coil, a cap secured to the lower end of the mass, aspring in said cap against which said plunger bears, a fiat springinterposedbetween the top of the plunger and the top of. the mass, thedegree of flexure of which is varied by movement of the top of theplunger with respect to the topof the mass, and means operative by themovement of the flat spring for controlling the circuit with which thedevice is associated.

22. A thermostatic device comprising an annular metallic body, a rodhaving a dif ferent coefiicient of expansion than the body arrangedwithin the body and supported therein at its lower end and an electricheating element embedded in 'said body.

23. A thermostatic device comprising an annular body of substantiallypure meta-l having a large coeflicient of expansion, a rod disposedwithin said body and supposed within the the apparatus and in closethermal communication with said device, said device and heating coilbeing proportioned so that they follow the heat curve of the apparatus,means operative by an increase in temperature of said device to apredetermined temperature to open the circuit, and means operative by anincrease in the magnetic flux of said coil to a predetermined value tocontrol the circuit with which the device is associated.

In testimony whereof, I have hereunto set my hand at San Francisco,California, this 2nd day of December, 1919.

ADONALD K. LIPPINCOTT. In presence of- H. G. PRQST.

